Yes, vampires can die if you expose them on the sun too much. After Heating up they will get Too much Sun moodlet, then Tjirst bar will drop much faster then normal. If bar will get empty they'll just turn into dust and ash.

Is there any possibility of making a version without the faster thirst decay, but with the changes in the buffs and mood value? That was the version I used with Showtime, since I don't really want all the NPC vampires dying from carelessness, but I like the other changes you did.

Hi. This mod is already updated to 1.55. You can go here: http://tremerionsims3.blogspot.com/2013/06/update-155-also-island-paradise.html to download it. You can always go to Updates section to check if mods are updated :)